1. Field of the Invention
The present invention relates generally to the binding of catalysts to solid supports and to functional polymeric materials, and to the derivatization and patterning of surfaces and processes and compositions for electroless metallization and related articles of manufacture. More particularly, the invention relates to the derivatization of surfaces using ligating chemical agents comprised of polymers capable of both bonding to a substrate and ligating with metal ions, metal complexes, nanoparticles or colloids for use in catalytic reactions. The present invention also relates to the use and patterning of ligating chemical agents and selective electroless plating through the use of such ligating agents, and derivative articles produced thereby.
2. Description of the Prior Art
It is often a goal, in areas such as organic and inorganic chemical catalysis, electronics and microelectronics, and electrochemistry, to efficiently bind to surfaces chemical activating agents, such as metal complexes, metal colloids, metal ions, and metal nanoparticles. In the field of microelectronic devices, sensors, optical elements and electronic displays, and the like, the development of inexpensive and convenient methods of fabrication is important. Of particular interest is the development of inexpensive and convenient methods to fabricate metal circuitry, which is found in each of the aforementioned applications.
In organic and inorganic chemical catalysis, it is desirable to recover catalysts from reaction products in an economically and environmentally sound manner. In conventional practice, catalysts have principally been applied in homogeneous form, in solution in an organic reactant phase. As such, their use has suffered from the difficulties inherent in the recovery of homogeneous catalysts from the reaction products. The recovery of catalyst from the reaction products is a relatively expensive operation and greatly increases the cost of the process. One approach is to immobilize the metal catalyst on a solid support; such a strategy is being investigated for use in organic chemical reactions, for example acylations, alkylations, enolate additions, Wittig reactions, Heck reactions, reductions, oxidations, etc., that are traditionally carried out in homogeneous solution.
One approach to catalyst immobilization for organic chemical catalysis involves coordinating a metal catalyst to a polymeric substrate. An early contribution in this direction was made by Grubbs et al. as reported in J. Am. Chem. Soc. 93, 3062 (1971). These authors chloromethylated slightly crosslinked polystyrene and reacted the resulting chlorine-containing polymer with lithium diphenylphosphide to produce a ligand-substituted polystyrene. Combination of the modified polymer with Wilkinson's catalyst (tris(triphenylphosphine)rhodium chloride), by coordination, produced an active, readily isolated, heterogeneous catalyst. Utility as a hydrogenation catalyst was demonstrated.
U.S. Pat. No. 3,652,678 to Allum et al. and U.S. Pat. No. 3,987,009 to Young disclose similar heterogeneous catalysts employing various insolubilizing polymers.
U.S. Pat. No. 3,998,887 to Allen discloses catalysts of similar type which comprised a polymer derived from p-styryldiethylphosphine.
U.S. Pat. No. 4,045,493 to Trevillyan discloses such catalysts comprising a polyphenylene polymer backbone and pendant diphenylphosphine ligand groups.
British Pat. No. 1,517,552 discloses a process for preparing other catalysts insolubilized by covalent attachment to various polymers. The catalysts of this patent are characterized by diphosphine bidentate ligands.
Chernyshov et al. in Chem. Mater. 12, 114 (2000) describe the immobilization of palladium species using block copolymers comprising polystyrene and poly-m-vinyltriphenylphosphine. These copolymers were also used to immobilize palladium nanoparticles.
Bianchini et al. in Chem. Comm. 479 (2001) describe the immobilization of a rhodium cyclooctadiene moiety using a copolymer of a styrene-functionalized tripodal phosphine and styrene/divinylbenzene.
Chan et al. in Chem. Mater. 4, 24 (1992) and J. Am. Chem. Soc. 114, 7295 (1992) describe the immobilization of metal nanoparticles in diblock copolymers. The copolymers were synthesized from diphosphine-functionalized norbornene monomers and methyltetracyclododecene.
Other inventors have produced immobilized catalysts by attachment of monomeric ligand groups to inorganic solids. For example, U.S. Pat. No. 3,907,852 to Oswald et al. discloses a process for preparing heterogeneous rhodium catalysts comprising silylhydrocarbyl phosphine ligands attached to silica and metal oxides.
U.S. Pat. No. 3,832,404 to Allum et al. discloses a hydroformylation process employing various catalysts, among others a rhodium catalyst comprising a monodentate phosphine ligand attached to inorganic solids containing a hydroxyl group. Silica was a preferred solid. The catalysts were prepared by addition of diphenylphosphine to triethoxyvinyl silane to form an intermediate which was combined, for example, with cyclo-octadiene rhodium chloride to produce a rhodium complex. The complex was attached to silica by ester exchange.
Bianchini et al. in Organometallics 19, 2433 (2000) describe the immobilization of various rhodium catalysts using a sulfonate-functionalized tripodal phosphine. The sulfonate group is used to bind the ligated rhodium catalyst to silica substrates via hydrogen bonding.
The above-described methods typically are relatively time-consuming. Bifunctional molecules, such as ligand-bearing silane adhesion promoters and other molecules comprising a group to ligate to the metal catalyst and a group to bind to a substrate surface, can be difficult to synthesize; many such materials require multi-step synthesis. Silane adhesion promoters are inconvenient to work with because they must be protected from moisture to prevent self-condensation. Polymeric materials for catalyst immobilization contain functional groups, preferably phosphines, to bind to the metal catalyst, but phosphine groups typically do not bind to a substrate surface. Thus, the catalyst complex or nanoparticle can be immobilized within the phosphine-bearing polymer but is not readily attached to a solid substrate.
In the fabrication of microelectronic devices, optics, and the like, it is desirable to deposit metal pathways on a surface in an economically and environmentally sound manner. A well-known method of production of such circuitry is photolithography. According to this technique, a negative or positive resist (photoresist) is coated onto the exposed surface of a substrate. The resist is then irradiated in a predetermined pattern, and irradiated (positive resist) or nonirradiated (negative resist) portions of the resist are washed from the surface to produce a predetermined pattern of resist on the surface. This is followed by one or more procedures. For example, the resist may serve as a mask in an etching process in which areas of the material not covered by resist are chemically removed, followed by removal of resist to expose a predetermined pattern of the conducting metal on the substrate. According to another example, the patterned surface is exposed to a plating medium or to metal deposition (for example under vacuum), followed by removal of resist, resulting in a predetermined plated pattern on the surface of the material. In addition to photolithography, x-ray and electron-beam lithography have found analogous use.
Other techniques for applying metal pathways to surfaces include the well-known “silk-screening” technique, in which a paste containing finely-divided metal particles in a carrier is applied, for example, via a screen including a pattern, to a substrate in a pattern corresponding to the screen pattern. The paste is fired and a conductive metal pathway having a pattern corresponding to the screen pattern results.
Electroless deposition is a process widely used for the application of metals such as copper, nickel, gold, silver, palladium, cobalt, and others to substrates. Electroless deposition occurs by an autocatalytic redox process, in which the cation of the metal to be deposited is reduced by a soluble reductant at the surface of a catalyst used to initiate the deposition, and subsequently at the metal feature being formed. This redox process generally takes place only on catalytic surfaces, that is, surfaces that inherently are catalytic to the redox process or surfaces that first are activated with a catalyst. Low-cost methods to pattern a catalyst on a non-catalytic substrate, that is, to selectively activate a substrate in a pattern corresponding to an ultimate pattern of metal deposition, are of interest.
For electroless plating, several methods are known for binding a catalyst to a non-catalytic substrate. Many methods use ligand-bearing silane adhesion promoters, for example, U.S. Pat. No. 5,389,496 to Calvert et al.; U.S. Pat. No. 5,510,216 to Calabrese et al.; and U.S. Pat. No. 5,648,201 to Dulcey et al. describe the chemisorption of ligand-bearing silane adhesion promoters onto a surface, application to the surface of Pd(II) solution to immobilize the Pd(II) species at the ligand via coordination, and immersing the substrate in an electroless plating solution to deposit a metal.
Other methods use thin polymer layers capable of binding a catalyst, for example, U.S. Pat. No. 4,701,351 to Jackson describes binding a catalyst to a non-catalytic substrate by coating the substrate with a thin layer of a polymer having the ability to complex with a noble metal compound, such as polyamines, polyacids, and the salts of polyacids; and immersing the substrate in a solution of an electroless plating catalyst which is bound to the polymer layer.
Several methods are known for patterning a catalyst on a non-catalytic substrate. That is, selectively activating a substrate in a pattern corresponding to an ultimate pattern of metal deposition. U.S. Pat. No. 4,472,458 to Sirinyan et al. describes a process for the production of metallized semiconductors using a process involving application of catalyst across a surface, applying a polymeric material, through a mask having a pattern, to the surface, plating a metal on the surface, and dissolving the template to produce a patterned metal layer.
U.S. Pat. No. 4,322,457 to Baron et al. describes patterned metal deposition that involves applying a surfactant to a substrate in a pattern (via, for example, conventional printing techniques) applying a precursor of a catalytic agent to the surface (e.g. Pd2+), allowing the precursor to the “buried” such that the surfactant covers the precursor in the originally-applied pattern, rinsing the surface, exposing the surface to an agent to convert the precursor to a catalyst (e.g. Pd), and plating a metal at the surface in a pattern complementary to the original pattern.
U.S. Pat. No. 4,192,764 to Madsen describes patterned metal deposition that involves coating a surface with a reducible salt of a non-noble metal and a radiation-sensitive reducing agent, irradiating the surface in a pattern to reduce the metal salt to a reduced catalyst in a pattern corresponding to the pattern of irradiation, and plating a metal at the pattern exposing the catalyst.
U.S. Pat. Nos. 3,873,359; 3,873,360; and 3,900,614 to Lando describe patterned metal deposition involving, according to a first embodiment, coating a substrate with a colloidal wetting solution capable of converting a catalyst precursor, such as palladium chloride, to a catalyst, using a stamp having a raised pattern to transfer to the surface the catalyst precursor so that the precursor reacts at the surface to form the catalyst in the pattern, and plating metal at the surface at the patterned catalytic region. According to a second embodiment, the method involves coating the surface with a catalyst precursor such as palladium chloride, using a stamp to transfer to the surface a reducing agent that converts the precursor to the catalyst in a pattern corresponding to the stamp pattern thereby reacting the precursor, in the patterned region, to produce the catalyst, and plating the metal at the surface in the pattern. According to a third embodiment, the method involves transferring to the surface, in a pattern, a reducing agent capable of reacting with a catalyst precursor to form a catalyst, exposing the surface to a catalyst precursor whereby a reaction occurs forming the catalyst in the pattern, and plating metal on the surface in the pattern.
U.S. Pat. No. 6,060,121 to Hidber et al. describes a method of transferring a colloidal catalyst to a surface involving pre-treatment of a surface with a ligand-bearing silane adhesion promoter to immobilize the colloidal catalyst, then transfer of a colloidal catalyst using an elastomeric stamp as an applicator, in a microcontact printing process.
U.S. Pat. No. 5,389,496 to Calvert; U.S. Pat. No. 5,510,216 to Calabrese; and U.S. Pat. No. 5,648,201 to Dulcey describe the chemisorption of ligand-bearing organosilanes onto a surface, deep UV irradiation through a patterned mask to selectively remove the organosilane in the pattern, application to the surface of Pd(II) solution to immobilize the Pd(II) species at the regions at which the ligand remains, and electroless deposition of a metal at those regions.
The above-described methods typically are relatively time-consuming and expensive in that they involve several steps including, for example, prior to plating a metal in a pattern at the surface, carrying out a chemical reaction at the surface, to convert a precursor to a reactant needed in the plating reaction, and/or involve relatively expensive equipment such as photolithographic apparatus, and/or involve the consumption of chemical reactants and generation of corresponding chemical waste to an undesirable extent. While U.S. Pat. No. 6,060,121 to Hidber et al. avoids many of these difficulties, the process described therein requires a separate surface treatment step to cause adhesion of the plated metal film to the surface prior to patterning, and the catalysts and, more particularly, the solvents in which they are dissolved are often detrimental to the microcontact printing applicator. For example, solutions of high or low pH may damage the surface of the stamp and reduce the number of times it may be used, other solvents readily absorb into the stamp material, swelling it and thus distorting the stamp pattern. The type of catalyst used is thus critical to this process. Commercially available palladium/tin catalysts, commonly used in manufacturing, cannot easily be used.
The above-described materials for catalyst immobilization are also inconvenient to apply to a surface using microcontact printing, for example, in patterned electroless metallization. Silane adhesion promoters form crosslinked structures in solution or on the surface of a stamp used for microcontact printing. Other materials often can only be dissolved in solvents that are detrimental to the microcontact printing applicator. For example, solutions of high or low pH may damage the surface of the stamp and reduce the number of times it may be used, other solvents readily absorb into the stamp material, swelling it and thus distorting the stamp pattern.
Accordingly, a general purpose of the present invention is to provide ligating copolymers which are capable of binding to a substrate surface and capable of ligating to a metal catalyst. Another purpose of the present invention is to provide a convenient synthetic strategy for such ligating copolymers, which renders unnecessary at least some of the above-described procedural steps, time, and expense. Another purpose of the present invention is to provide a method for the immobilization of catalysts on a substrate surface. Another purpose of the present invention is to provide ligating copolymers which are soluble in solvents compatible with applicators used in microcontact printing. Another purpose of the invention is to provide a method for selective electroless metallization that uses ligating chemical agents, which are soluble in solvents compatible with applicators used in microcontact printing, and which are capable of binding to a substrate surface and capable of ligating to an electroless plating catalyst. Another general purpose of the invention is to provide a method for selective electroless metallization that allows for the use of a variety of electroless plating catalysts. Another general purpose of the invention is to provide a method of conveniently, quickly, inexpensively, and reproducibly applying to a surface such a chemical ligating agent in a manner that renders unnecessary at least some of the above-described procedural steps, reactants, waste products, time, and expense. Another purpose of the invention is to produce a variety of metal patterns on surfaces without these complications. Another purpose of the invention is to provide metal pathways on substrates that are conveniently and inexpensively manufactured.